Looking Up: Mount up with wings of the Eagle

Viewing bald eagles has become almost a patriotic event. America’s national bird inspires great awe as one soars overhead or is spotted resting on a branch.

Where this column originates, Honesdale, Wayne County, Pa., is near a large number of eagles, many which spend the winter on the Upper Delaware. If actual eagles are not a common sight, you can always enjoy the Eagle constellation, riding high in the summer night.

Its Latin name is Aquilia. Tracing the imagined lines between several prominent stars, it is not hard to picture the great bird. Its brightest star, Altair, marks the eye. Whether it is meant to have white head feathers, making it a “bald” eagle, is not clear.

In Greek mythology, Aquilia carries the lightning bolts dispatched by Zeus, and gives a ride to the shepherd boy Ganeymede. Persian, Hebrew, Arab, Greek and Latin tradition all knew this star group as the Eagle.

To find Aquilia the Eagle in late July or early August, look south-southeast soon after the sky darkens.

If you're fortunate to live in or visit an area where light pollution is not a big problem, on a moonless night the hazy Milky Way Band will be seen rising from the southern horizon, reaching nearly overhead and back down in the northeast.

Aquilia lies in the midst of the Milky Way, about halfway up the south-southeast sky. Altair is easy to spot; it is brighter than 1st magnitude and is sandwiched between two easily seen stars to the lower left and upper right. These mark the beak and head.

Astronomers have found that Altair rotates so quickly, the star is flattened at the poles. It lies about 16 light years from the sun, meaning the light you see from Altair tonight left the star in 1992.

Its apparent magnitude is +1.77; star light is ranked on scale with 6th magnitude being the average limit the unaided eye can detect, and the brightest stars in the night sky, at magnitude +1 and brighter (why the brightest star in the night doesn’t begin the scale is a good question).

Altair’s “absolute magnitude” is +2.2, which is a standard astronomers use to classify stars by their true light output. Absolute magnitude is the brightness a given star would appear if it were a distance of 10 parsecs. One parsec is equal to 3.3 light years. A light year is the distance light travels in one year’s time.

By comparing stars this way, we can judge at a glance whether they are 40 watt or 100 watt bulbs, so to speak. The sun’s absolute magnitude is only +4.8, so Altair packs more power. The sun, though, takes the prize and literally makes the day, being our closest (and dearest) star; its apparent magnitude is MINUS (-) 27!

Having the Milky Way in the background means the constellation is home to many wonderful star fields, star clusters and nebulous wisps, hunted down by backyard telescope enthusiasts. In 1918, a nova erupted in Aquilia, briefly outshining Altair.

Near the Eagle’s tailfeather stars is a majestic star cluster waiting your attention with binoculars or a telescope of any size. This cluster, known in celestial catalogs as “M11,” has a more interesting nickname, the “Wild Duck Cluster.” Thus, we have ducks on the tail of the eagle.

M11 is technically just over the artificial boundary of Aquilia and is part of the constellation Scutum the Shield. It is an amazing sight in a telescope, even at low magnification.

You will see a densely packed patch of stars, its shape left to your imagination. Some see a formation of wild ducks. Its most concentrated area has an unusual rectangular appearance, with a couple dark voids within, containing few noticeable stars. In binoculars you will see is a small, fuzzy patch in a rich starry field.

The Milky Way Band also has a great many apparent dark voids, which are actually regions of nebulous clouds masking the stars behind them. They take on many shapes for our imagination. One that is visible in binoculars and even unaided eyes on an exceptional night, is distinctly shaped like a capital letter “E” and is located just west of Altair. A very clear, dark night is essential.